Various types of hydraulic machines are in use today. In particular, gerotor machines are known, i.e. a type of machine to which the present invention specifically refers. U.S. Pat. No. 3,453,966 discloses a hydraulic machine which can be used as a motor or as a hydraulic pump. A stationary outer gerotor element is provided which cooperates with a rotating inner gerotor element. When used as a pump, the inner gerotor element is driven via gear means by a shaft. This known hydraulic machine requires high manufacturing cost and rotating discs are required to control the supply and discharge of a pressure medium.
DE-OS No. 20 10 524, DE-AS No. 11 38 639 and U.S. Pat. No. 3,302,584 all disclose hydraulic machines using rotary control elements or control discs for controlling the flow of pressure medium. According to DE-OS No. 20 10 524 the discharge of pressure medium occurs via the rotating shaft. This requires the transfer of pressure medium from a stationary to a movable component which is not without problems.
Moreover, numerous hydraulic machines are known using rotating compression chambers with the result that stationary discs have to be used for supplying and removing pressure medium.
It is an object of the present invention to provide a hydraulic pump having a stationary outer gerotor element and a cooperating rotating inner gerotor element in such a manner that the amount of pressure medium supplied by the pump is limited with the consequence that the energy requirements of the pump are favourable, low manufacturing costs are achieved, and a good long-time operating performance can be maintained.
It is another object of the invention to provide a hydraulic pump for the power steering of a car such that the power requirement of the pump matches the requirements of the power steering apparatus so that only low losses of power occur in the pump.